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Biology Mock AS 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is dynamic equilbrium

A

internal environment of the body fluctuating around a specific normal level

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2
Q

what are the 3 things homeostasis is important for

A

temperatrue
blood glucose
water

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3
Q

how is homeostasis important for temperature

conditions where it will cause enzyme to denature

A

ensures the maintenance of optimal conditions for enzyme action and cell function

an increase in body temperature above 40 °C would cause enzymes to denature

This is due to an increase in kinetic energy which would result in the breakage of hydrogen bonds holding the enzyme in a specific 3D shape

The active site will change shape and will no longer be complementary to the substrate molecule

An enzyme-substrate complex cannot form and the enzyme cannot catalyse that reaction anymore, leading to less efficient metabolic reactions

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4
Q

how is homeostasis important for blood glucose

A

Cells also need a constant supply of energy in the form of ATP to work efficiently

Glucose is respired to supply this ATP, meaning that the body needs to carefully monitor and control blood glucose concentrations

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5
Q

how is homeostasis important for water

A

crucial for the amount of water in the blood to remain constant
Water is lost during excretion of waste products, e.g. urine, and in sweat
The kidneys are responsible for regulating the amount of water in the blood

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6
Q

what is the control mechanism for maintaining body temperature

A

thermoregulation

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7
Q

how is vasodilation a cooling mechanism

A

Vasodilation of the blood vessels that supply skin capillaries, supplying the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation

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8
Q

what the cooling mechanisms

A

Vasodilation of the blood vessels
Sweating
Flattening of hairs

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9
Q

how is sweating a cooling mechanism

A

Sweat is secreted by sweat glands
This cools the skin by evaporation; heat energy from the body converts liquid water into water vapour

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10
Q

why is sweating less of an effective cooling mechanism during humid conditions

A

sweat evaporates more slowly due to a reduced concentration gradient between the sweat and the surrounding air

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11
Q

how is flattening of hair a cooling mechanism

A

The hair erector pili muscles in the skin relax, causing hairs to lie flat
These muscles can be described as effectors, as they respond to a change in body temperature
This stops them from forming an insulating layer of trapped air and allows air to circulate over skin; heat can therefore leave by radiation

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12
Q

what are warming examples

A

Vasoconstriction of blood vessels that supply skin capillaries

Boosting metabolic rate

Shivering

Erection of hairs

Less sweating

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13
Q

how is vasoconstriction of blood vessels a warming mechanism

A

During vasoconstriction the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through skin capillaries

Instead, the blood is diverted through shunt vessels, which are deeper in the skin and therefore do not lose heat to the environment

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14
Q

how is boosting metabolic rate a warming mechanism

A

Most of the metabolic reactions in the body are exothermic and this provides warmth to the body

In cold environments the hormone thyroxine, released from the thyroid gland, increases the basal metabolic rate (BMR), increasing heat production in the body

Adrenaline may also be released to speed up the metabolic rate and release more heat

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15
Q

how is shivering a warming mechanism

A

This is a reflex action in response to a decrease in core body temperature
This means it is a nervous mechanism, not a hormonal one

In this case muscles are the effectors and they contract in a rapid and regular manner
The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature

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16
Q

How is the erection of hairs a warming mechanism

A

The hair erector pili muscles in the skin contract, causing hairs to stand on end

This forms an insulating layer over the skin’s surface by trapping air between the hairs and stops heat from being lost by radiation

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17
Q

how is less sweating a warming mechanism

A

The sweat glands will secrete less sweat when it is cold

This will reduce the amount of heat lost through the evaporation of sweat

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18
Q

role of the hypothalamus in thermoregulation

A

Mammals detect external temperatures via thermoreceptors found in the skin and mucous membranes

There are receptors for both heat and cold
These communicate with the hypothalamus along sensory neurones

The hypothalamus will send impulses along motor neurons to effectors to bring about a physiological response to changing external temperatures

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19
Q

does hypothalamus help regulate body temperature

A

Yes, by monitoring the temperature of the blood flowing through it and initiating homeostatic responses when it gets too high or too low

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20
Q

what is a negative feedback system

A

reversing a change in the body to bring it back within normal limits

If body temperature rises a negative feedback system will act to lower body temperature, bringing it back to normal
If blood glucose levels drop a negative feedback system will act to raise blood glucose, bringing it back to normal

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21
Q

describe a negative feedback control loop

A

A receptor detects a stimulus that is involved with a physiological factor
E.g. a change in temperature or blood glucose level

A coordination system transfers information between different parts of the body
- This could be the nervous system or the hormonal system

An effector carries out a response
Effectors are muscles or glands

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22
Q

what is positive feedback

A

the original stimulus produces a response that causes the factor to deviate even more from the normal range

23
Q

how can hormones alter events inside a cell

A

by influencing gene expression

24
Q

how do eukaryotes control gene expression

A

using transcription factors

25
Q

what is a transcription factor

A

a protein that controls the transcription of genes by binding to a specific region of DNA

26
Q

what are activators and repressors

A

transcription factors that increase the rate at which a gene is expressed

transcription factors that decrease the rate at which a gene is expressed

27
Q

what are hormones that are able to cross cell surface membrane able to do

A

enter the nucleus and bind to transcription factors that are present there

28
Q

explain hormonal regulation of body temperature

A

At normal body temperature a transcription factor known as the thyroid hormone receptor binds to a section of DNA at the start of a gene

This gene codes for a protein that increases the metabolic rate, generating more heat and therefore increasing body temperature

As long as the thyroid hormone receptor is bound to the region of DNA at the start of the gene, the gene will not be expressed; it can be said to be switched off

29
Q

in cold temperature what will the body release

A

the hormone thyroxine which binds to the thyroid hormone receptor

Once the hormone and the receptor are bound together the thyroid hormone receptor allows RNA polymerase to bind to the start of the gene; the gene is said to be switched on and its rate of expression will increase

The protein which increases the metabolic rate is produced in larger quantities, leading to an increase in body temperature

30
Q

what do hormones that cannot cross the cell membrane do

A

bind to receptors in the cell surface membrane

The binding of these hormones to cell surface membrane receptors activates second messengers

The activated second messenger molecules activate protein kinases enzyme
Active protein kinase enzymes trigger a chain of reactions, known as a cascade, inside the cell

The cascade may result in changes to the activity of transcription factors which may then affect gene expression in the cell

31
Q

what are the examples of the hormones that bind to receptors in the cell surface membrane

A

Adrenaline
Insulin
Glucagon
ADH

32
Q

what is the control of the heartbeat known as

A

myogenic, which means the heart will beat without any external stimulus

33
Q

explain the electrical activity in the heart starting from the SAN

A

The SAN initiates a wave of depolarisation that causes the atria to contract

the depolarisation is prevented from spreading straight to the ventricles due to the non conduction tissue

Instead, the depolarisation is carried to the atrioventricular node (AVN)

This is a region of conducting tissue between atria and ventricles

After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His

The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them

Purkyne fibres spread around the ventricles and initiate the depolarisation of the ventricles from the apex (bottom) of the heart

This makes the ventricles contract from the bottom upward and blood is forced out of the ventricles into the pulmonary artery and aorta

34
Q

what is the SAN

A

a group of cells in the wall of the right atrium

35
Q

events of the cardiac cycle

A

Sinoatrial node sends out a wave of excitation

Atria contract

Atrioventricular node sends out a wave of excitation

Purkyne tissue conducts the wave of excitation

Ventricles contract

36
Q

what can be used to monitor the electrical activity of the heart

A

Electrocardiography

37
Q

explain how to carry out electrocardiography

A

Electrodes that are capable of detecting electric signals are placed on the skin
These electrodes produce an electrocardiogram (ECG)
An ECG shows a number of distinctive electrical waves produced by the activity of the heart

38
Q

draw the ECG of a healthy heart and label each wave and why it is caused
PQRSTU

A

The P wave
Caused by the depolarisation of the atria, which results in atrial contraction (systole)
The QRS complex
Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)
This is the largest wave because the ventricles have the largest muscle mass
The T wave
Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)
The U wave
Scientists are still uncertain of the cause of the U wave, some think it is caused by the repolarisation of the Purkyne fibres

39
Q

what does the bigger the wave on the ECG represent

A

the greater the electrical activity passing through the heart, which results in a stronger contraction

40
Q

what is tachycardia

A

When the heart beats too fast it is tachycardic

resting heart rate of over 100 bpm

41
Q

what is bradycardia

A

When the heart beats too slow
resting heart rate below 60 bpm

42
Q

what is ectopic heartbeat

A

early heartbeat followed by a pause

This could be due to an earlier contraction of either the atria or ventricles

43
Q

what is fibrillation

A

An irregular heartbeat will disrupt the rhythm of the heart
The atria or ventricles stop contracting properly

44
Q

what is cardiac output

A

volume of blood that is pumped by the heart per unit of time

45
Q

what is the average cardiac output

A

4.7 litres of blood per minute when at rest

46
Q

why does cardiac output increase when an individual is exercising

A

so that the blood supply can match the increased metabolic demands of the cells

47
Q

how can CO be calculated

A

Cardiac output = heart rate x stroke volume

Cardiac output is measured in cm3 min-1
Heart rate is measured in beats per min (bpm)
Stroke volume is measured in cm3

48
Q

what is stroke volume

A

volume of blood pumped out of the left ventricle during one cardiac cycle

49
Q

what is bundle of his

A

a collection of conducting tissue in the septum (middle) of the heart

50
Q

describe how thermoregulatory mechanisms are controlled to help marathon runners avoid heat stress

A

thermoreceptors (in
hypothalamus or skin) detect increase in temperature
{ heat loss / thermoregulatory } centre in hypothalamus stimulated
* (hypothalamus) sends impulses to sweat glands (1)
.
increased blood flow to surface of skin by
{vasodilation / constriction of shunt vessels}
* decreased metabolic rate

51
Q

parasympathetic and sympathetic

A

parasympathetic - rest and digest
sympathetic - fight or flight

52
Q

Explain the role of the nervous system in bringing about the increase in temperature of the fingertip

A

thermoreceptors detect increase in temperature (1)

  • description of role of hypothalamus in heat loss mechanism (1)
  • (therefore more) impulses are sent along the sympathetic {nerves / nervous system } (1)
  • which leads to constriction of shunt vessels (1)
  • therefore causing vasodilation (of arterioles) (1)
  • so more warm blood flows near the skin surface (1)
53
Q
A

Biology Mock AS 2 (23 decks)

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